Patent DE 3620151 A1 describes a bending device where two suspended articulated robots are employed, between which a rigidly and stationarily arranged clamping unit is provided, which enables rotation of the workpiece about the workpiece's longitudinal axis. In this case, the workpieces are picked up, either by means of a pivotable feeding unit or by the bending robots, from the conveyor belt of a supplying means and are transferred to the clamping unit. The workpiece can be deposited in a subsequently arranged receiving means after bending has been performed. In this disclosed bending machine, processing of a clamped elongated workpiece, e.g. of a pipe, is not possible at the clamping location due to the rigidly fixed clamping unit. Otherwise, the workpiece would have to be displaced in a longitudinal direction for this purpose, which involves a considerable complication. Moreover, the suspended arrangement of the articulated robots requires a relatively large support from which the articulated robots can be suspended. Finally, simultaneous insertion and deposition of workpieces is not possible with the bending machine disclosed in patent DE 3620151 A1. Also, additional securing or clamping of long workpieces is not provided therein.
The bending machine disclosed in DE 3922326 C2 as well as in EP 0 934 783 B1 is provided with two articulated robots, each of the robots arranged on its own guideway in a longitudinally displaceable manner. The guideways are parallel to each other and have arranged between them a gripping unit which can be vertically displaced and pivoted away downwardly. However, it is disadvantageous in the DE 3922326 C2 and EP 0 934 783 B1 bending machine that three separate guides are needed and the gripping unit is again stationary and not displaceable. Bending robots always have to be employed for handling the workpiece to be processed, which means a reduction in the performance of the entire machine. Moreover, stable securing of the workpieces, particularly of longer workpieces, cannot be ensured without additional gripping clamps. The bending heads on the bending robots likewise enable only the draw bending method.
DE 19628392 A1 describes a bending machine wherein two bending towers and a central gripping unit are mounted on a machine bed. The bending towers as well as the gripping unit can be moved on the machine bed. Bending heads, which are rotatable about the workpiece axis, are mounted to the bending towers. However, this disclosed bending machine only allows bending operations to be effected in the workpiece axis, which requires additional feed and pick-up units. Moreover, a great number of gear elements are needed to actuate the bending heads, and the gripping unit limits the free bending space in the working area of the machine.
The bending machine of DE 601 00 147 T2 uses two gripping units, which enables bending also of lines having a flexible portion. For this purpose, each gripping unit is provided with two grippers which can grip on both sides of a flexible part. The bending head is mounted to a kind of robot which may have very different designs. During operation, the first gripping unit takes the workpiece from a supplying unit and pivots it into the working area (bending area) of the bending machine. There, the first half of the workpiece is bent. The workpiece can then be rotated around 180° by the second gripping unit, after which the other half of the workpiece can then be provided with bends. Since, due to the presence of only one bending head, the two halves of the workpiece can only be bent one after the other, but not at the same time, this disclosed bending machine has relatively low performance. Moreover, the bending head employed enables only the draw bending method. In addition, the entire machine has a very complicated structure.
A handling means for rods in a bending system is disclosed in DE 603 01 913 T2. There, two grippers are mounted to a portal, on which they can be moved in space. Moreover, the grippers are pivotable about an axis which is parallel to the workpiece axis. Further, the bending heads are movably mounted on a guide bed. However, the portal construction of the transport means requires a large amount of space. Moreover, the grippers cannot be moved independently of each other to the supplying means (magazine), which in turn reduces the efficiency of the disclosed machine.
In the bending machine of DE 10 2004 012 297 A1, a multiplicity of bending stations are used in sequence, which are suspended from above, which require a relatively large support. In this case, several pivoting grippers are provided for transferring the workpieces between the individual bending stations, with the gripping mechanism tracing a curved path so as to pick up the pipe from the previous station and to pass it on to the subsequent station after bending. In addition to the large support, the bending machine also has the disadvantage that no additional support of the workpiece is provided apart from the respectively employed pivoting gripper.
Finally, a bending machine for processing workpieces in several stations is disclosed in DE 20 2004 011 947 U1, wherein each station comprises a central gripping unit and two bending heads arranged laterally of said gripping unit. The bending heads and the gripping unit are each displaceable on a common guide bed. Additionally, a pivotable transfer device is also provided by which each workpiece can be pivoted from the first station to the second parallel station. This transfer device can simultaneously also constitute the gripping unit. The machine works serially from out of a magazine. Due to the almost closed, round bending head disk of the disclosed bending machine, however, bends of more than 90° are not possible, and in some cases a cantilever is even used as the bending tool. This produces long, straight portions in the middle of a workpiece. The employed bending head only enables roll bending.